Several prior suggestions have been made for recovering methyl esters of aromatic acids and glycols from thermoplastic polyester scrap using methanolysis, i.e., treating the polyester polymer with methanol, such as U.S. Pat. Nos. 5,504,122 (Michel et al), 5,393,916 (Gamble et al), 5,391,263 (Hepner et al), 5,051,528 (Naujokas et al), and EP 484,963 (DuPont-Michel), and in art references cited therein. Further improvements would be desirable in view of the commercial importance of polyester polymers and the increasing need to recover their chemical precursors from polyester scrap. Ethylene terephthalate polymers have been the polyester polymers that have been used commercially for the most part, and so these polymers and their chemical precursors, ethylene glycol (EG), terephthalic acid (TPA) and dimethyl terephthalate (DMT), so are the polyester polymers mainly discussed hereinafter, but the invention is believed applicable to other polyester polymers, for instance trimethylene glycol terephthalate (sometimes referred to as 3G-T, sometimes as PTT) and tetramethylene glycol terephthalate (4G-T).
Hepner et al U.S. Pat. No. 5,391,263 concerns a process for the separation of glycols from dimethyl terephthalate (DMT) involving distillation using methyl benzoate and/or the methyl ester of p-toluic acid (MPT) as an azeotropic agent. In particular, that process was applied to a mixture formed by the treatment of waste polyester with methanol to form DMT, EG and diethylene glycol (DEG) in which process, referring to Hepner's drawing, polyethylene terephthalate (PET) and DMT were heated and the resulting molten polymer mixture was treated with methanol (MEOH) vapor and depolymerized in a (methanolysis) reactor, from the reflux section of which a vapor mixture of MEOH, EG, DMT and DEG was passed to a methanol removal column. After removal of MEOH, the (rest of the) mixture was passed to an azeotrope column, and was treated with the azeotropic agent (MPT and/or methyl benzoate), the DMT being removed from the azeotrope column as bottoms and the resulting azeotropes being taken overhead to a vessel for separation into two phases, namely a phase rich in the azeotropic agent, which could be recycled to the azeotrope column, and a phase rich in glycols, which was passed to a distillation column to recover the desired glycols as bottoms and the azeotropic agent overhead.